In higher mammals, including humans, some examples of neural plasticity (e.g., the anatomical, physiological and behavioral consequences of monocular deprivation) seem to occur only within some critical or sensitive period in infancy. Other instances of sensory rearrangement, such as prism adaptation and some nerve-muscle crosses, seem to produce adaptive change in the behavior of both adults and infants. This is a proposal to study, in the same animals, both neural and behavioral changes which result from a particular type of sensory rearrangement, namely surgical torsional rotation of the eye, when performed in newborn kittens or in adult cats. If there are sensory "limits" to neural plasticity, then at least in kitten rotates, neurons of the visual cortex are expected to show compensatory changes (e.g., in interocular differences in preferred orientation) only when the angle of rotation is small and less change or noncompensatory change (e.g., loss of binocular connections), if any, when the angle if large. If such neurophysiological changes play any role in behavioral adaptation to a rotated visual world, then they should closely parallel careful behavioral measures of adaptation which will be obtained from the same animals. If only one eye is rotated, it also seems likely that the normal eye will exert some suppressive influence on the rotated eye under binocular viewing conditions. A number of behavioral tests for suppression will be conducted. It should then be possible to assess directly the extent to which such suppression, if it can be demonstrated, is paralleled by changes in cortical physiology.